hey alex, yes plants will rebud if the light cycle is right. how long has the other plant been under 12/12? some strains take longer to show flowers than others. if it has been longer than 2 weeks check for any light leaking in during the night cycle. you can also try to change the light cycle to 13/11 or 11/13 and see if that helps. some sativas flower with more hours of light than indicas.